The present invention relates to a detection system for displaying searched surrounding conditions and an area marker defining a selected geographical area on the display face of an indicator.
The present invention can be embodied in a radar apparatus or in a sonar apparatus.
Hereinafter, the present invention will be explained as embodied in a radar apparatus.
A prior art radar apparatus displays an area marker defining a selected geographical area of constant angular width and constant range depth on the screen of an indicator and activates a warning alarm when a target enters the area, as described in an unexamined Japanese patent publication No. 61-209380. With the prior art radar apparatus, a distance marker and a bearing marker are used to draw two arcs and two straight lines each connecting ends of the two arcs to form and indicate an area marker. First, the distance marker specifies a first range from the radar antenna, and the bearing marker specifies a first bearing. Then, the distance marker and bearing marker are moved on the display face of an indicator to specify a second range and a second bearing respectively to obtain an area marker formed with two arcs and two straight lines for defining a geographical area. Thus, bothersome operation is required to display an area marker on the display face of an indicator of the prior art radar apparatus.